Electrode Assembly

ABSTRACT

An electrode assembly includes a plurality of electrodes arranged in a stack along a stacking axis with a respective separator portion of an elongated separator sheet positioned between and winding around each of the electrodes in the stack along a serpentine path. The plurality of electrodes include a top electrode positioned at a top of the stack along the stacking axis, and the plurality of electrodes include a bottom electrode positioned at a bottom of the stack. The separator portions in the stack include a top separator portion abutting the top electrode and a bottom separator portion abutting the bottom electrode. The bottom electrode may have a thickness along the stacking axis that is from 80% to 120% of a thickness of the top electrode along the stacking axis. Moreover, a maximum thickness of each of the electrodes in the stack may be less than 8.3 mm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Korean Patent Application No.10-2021-0090598 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090588 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090589 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090590 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090591 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090592 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090596 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090597 filed on Jul. 9, 2021, Korean Patent Application No.10-2021-0090600 filed on Jul. 9, 2021, and Korean Patent Application No.10-2021-0090601 filed on Jul. 9, 2021, the entire contents of all ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electrode assembly.

BACKGROUND ART

Secondary batteries, unlike primary batteries, are rechargeable, andhave been widely researched and developed in recent years due to theirsmall size and large capacity. As technology development and demand formobile devices increase, the demand for secondary batteries as an energysource is rapidly increasing.

Secondary batteries can be classified into a coin-type battery, acylindrical battery, a prismatic battery, and a pouch-type battery,according to the shape of the battery case. In a secondary battery, anelectrode assembly mounted inside a battery case is achargeable/dischargeable power generating element having a stackedstructure comprising electrodes and separators.

The electrode assembly may be generally classified into a jelly-rolltype, a stack type, and a stack-and-folding type. In the jelly-rolltype, a separator is interposed between a sheet type positive electrodeand a sheet type negative electrode, each of which are coated with anactive material, and the entire arrangement is wound. In the stack type,a plurality of positive and negative electrodes are sequentially stackedwith a separator interposed therebetween. In a stack-and-folding type,stacked unit cells are wound with a long-length separation film.

SUMMARY OF THE INVENTION

The present invention provides, among other things, an electrodeassembly which has reduced deviations in adhesive force and airpermeability across each layer, while still maintaining adequateadhesive force and air permeability.

An exemplary aspect of the present invention provides an electrodeassembly. The electrode assembly in accordance with such aspect of theinvention preferably includes a plurality of electrodes arranged in astack along a stacking axis with a respective separator portionpositioned between each of the electrodes in the stack. The plurality ofelectrodes include a top electrode positioned at a top of the stackalong the stacking axis, and the plurality of electrodes include abottom electrode positioned at a bottom of the stack along the stackingaxis. The bottom electrode may have a thickness along the stacking axisthat is from 80% to 120% of a thickness of the top electrode along thestacking axis. Moreover, a maximum thickness of each of the electrodesin the stack may be less than 8.3 mm.

In accordance with some aspects of the invention, the separator portionsmay be portions of an elongated separator sheet. Such elongatedseparator sheet may be folded between each separator portion such thatthe elongated separator sheet follows a serpentine path traversing backand forth along an orthogonal dimension orthogonal to the stacking axisto extend between each of the successive electrodes in the stack.

The electrode assembly according to exemplary aspects of the presentinvention is desirably capable of preventing side-effects, such aslithium (Li) precipitation in the electrode assembly and non-charging ofthe electrode assembly. The electrode assembly according to the presentinvention is preferably also structurally stable and has high safety inuse.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an example of an electrodeassembly according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view of the electrode assembly of FIG. 1 ,illustrating positions of an upper surface, a lower surface, and amiddle portion of the electrode assembly.

FIG. 3 is a top plan view illustrating an electrode assemblymanufacturing apparatus for manufacturing the electrode assemblyaccording to the present invention.

FIG. 4 is a front elevation view conceptually illustrating the electrodeassembly manufacturing apparatus of FIG. 3 .

FIGS. 5 and 6 are photographs showing the results of checking whetherlithium (Li) is precipitated by disassembling the electrode assembliesof Comparative Example 1 and Example 1, respectively, after charging iscompleted.

FIG. 7 is a diagram schematically illustrating an electrode assemblymanufacturing method for manufacturing the electrode assembly accordingto the present invention.

FIG. 8 is a perspective view of a separator heating unit of a separatorsupply unit according to the exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

The objects, specific advantages, and novel features of the presentinvention will become more apparent from the following detaileddescription taken in conjunction with the accompanying drawings andexemplary embodiments. In the present specification, in adding referencenumbers to the constituent elements of each drawing, it should be notedthat the same constituent elements are given the same number even thoughthey are indicated on different drawings. In addition, the presentinvention may be implemented in several different forms and is notlimited to the exemplary embodiments described herein. Further, indescribing the present invention, detailed descriptions of related knowntechnologies that may unnecessarily obscure the gist of the presentinvention will be omitted.

FIG. 1 is a cross-sectional view illustrating an example of an electrodeassembly according to an exemplary embodiment of the present invention.That is, referring to FIG. 1 , an electrode assembly 10 according to anexemplary embodiment of the present invention includes a stack ofelectrodes in which one or more first electrodes 11 alternates with oneor more second electrodes 12. Each of the electrodes in the stack areseparated from one another by a separator 14 positioned therebetween,which may be a single elongated separator 14 repeatedly folded so as tofollow a serpentine or zigzag path around each successive electrode.

The electrode assembly 10 is a chargeable/dischargeable power generatingelement, where the first electrode may be a positive electrode, and thesecond electrode may be a negative electrode. However, alternatively,the first electrode may be a negative electrode, and the secondelectrode may be a positive electrode. Moreover, the electrode assembly10 may be provided in a form in which the outermost portion issurrounded by the separator 14, e.g., by wrapping the separator aroundthe assembled electrode assembly 10, as illustrated in FIG. 1 . Withrespect to the electrodes and the separator comprising the electrodeassembly, materials commonly used in the art may be used.

As discussed further herein, an “upper surface” of the electrodeassembly 10 refers to the uppermost position of the electrode assembly10 in the stacking direction of the electrode assembly, which isdesignated by reference numeral 2 in FIG. 2 . Thus, subsequentreferences to “upper surface air permeability” relate to airpermeability of the separator 14 abutting the uppermost electrode in theelectrode assembly. Likewise, subsequent references to “upper surfaceadhesive force” refer the adhesive force between the uppermost electrodein the electrode assembly and the abutting portion of the separator 14.

Further, as discussed herein, a “lower surface” of the electrodeassembly 10 refers to the lowermost position of the electrode assembly10 in the stacking direction of the electrode assembly, which isdesignated by reference numeral 3 in FIG. 2 . Thus, subsequentreferences to “lower surface air permeability” relate to airpermeability of the separator 14 abutting the lowermost electrode in theelectrode assembly. Likewise, subsequent references to “lower surfaceadhesive force” refer the adhesive force between the lowermost electrodein the electrode assembly and the abutting portion of the separator 14.

Finally, as discussed herein, the “middle” of the electrode assembly 10refers to a middle position between the upper surface and the lowersurface of the electrode assembly 10 in the stacking direction of theelectrode assembly, as designated by reference numeral 1 in FIG. 2 . Forexample, when an electrode assembly 10 formed of nine electrodes andviewed from the side, as in FIG. 2 , the “middle” position relates tothe position of the fifth electrode in the stack. Thus, subsequentreferences to “middle air permeability” relate to air permeability ofthe separator 14 abutting the middle electrode in the electrodeassembly. Likewise, subsequent references to “middle adhesive force”refer the adhesive force between the middle electrode in the electrodeassembly and the abutting portion of the separator 14.

Referring to FIGS. 3 and 4 , an apparatus 100 for manufacturing anelectrode assembly according to an exemplary embodiment of the presentinvention includes a stack table 110; a separator supply unit 120 forsupplying a separator 14; a first electrode supply unit 130 forsupplying a first electrode 11; a second electrode supply unit 140 forsupplying a second electrode 12; a first electrode stack unit 150 forstacking the first electrode 11 on the stack table 110; a secondelectrode stack unit 160 for stacking the second electrode 12 on thestack table 110; and a press unit 180 for bonding the first electrode11, the separator 14, and the second electrode 12 to each other.Further, the apparatus 100 for manufacturing the electrode assemblyaccording to the exemplary embodiment of the present invention mayinclude a holding mechanism 170 for fixing the stack (comprising thefirst electrode(s) 11, the second electrode(s) 12, and the separator 14)to the stack table 110 as the stack is being assembled.

The separator supply unit 120 may have a passage through which theseparator 14 passes towards the stack table 110. In particular, theseparator supply unit 120 may include a separator heating unit 121defining the passage through which the separator 14 passes towards thestack table 110. As shown in FIG. 8 , the separator heating unit 121 mayinclude a pair of bodies 121 a, each of which may be in the form of asquare block, and the bodies 121 a may be spaced apart by a distancedefining one of the dimensions of the passage through which theseparator 14 passes. At least one or both of the bodies 121 a mayfurther include a separator heater 121 b for heating the respective body121 a, and thereby transferring heat to the separator 14.

The separator supply unit 120 may further include a separator roll 122on which the separator 14 is wound. Thus, the separator 14 wound on theseparator roll 122 may be gradually unwound and pass through the formedpassage to be supplied to the stack table 110.

The first electrode supply unit 130 may include a first electrode roll133 on which the first electrode 11 is wound in the form of a sheet, afirst cutter 134 for cutting the first electrode 11 at regular intervalsto form the first electrodes 11 having a predetermined size when thefirst electrode 11 is unwound and supplied from the first electrode roll133, a first conveyor belt 135 for moving the first electrode 11 cut bythe first cutter 134, and a first electrode supply head 136 for pickingup (e.g., via vacuum suction) the first electrode 11 transferred by thefirst conveyor belt 135 and seating the first electrode 11 on a firstelectrode seating table 131.

The second electrode supply unit 140 may include a second electrodeseating table 141 on which the second electrode 12 is seated beforebeing stacked on the stack table 110 by the second electrode stack unit160. The second electrode supply unit 140 may further include a secondelectrode roll 143 on which the second electrode 12 is wound in the formof a sheet, a second cutter 144 for cutting the second electrode 12 atregular intervals to form the second electrode 12 of a predeterminedsize when the second electrode 12 is unwound and supplied from thesecond electrode roll 143, a second conveyor belt 145 for moving thesecond electrode 121 cut by the second cutter 144, and a secondelectrode supply head 146 for picking up (e.g., via vacuum suction) thesecond electrode 12 transferred by the second conveyor belt 145 andseating the second electrode on the second electrode seating table 141.

The first electrode stack unit 150 may be structured to stack the firstelectrode 11 on the stack table 110. The first electrode stack unit 150may include a first suction head 151 and a first moving unit 153. Thefirst suction head 151 may pick up the first electrode 11 seated on thefirst electrode seating table 131 via vacuum suction through one or morevacuum suction ports (not shown) formed on a bottom surface of the firstsuction head 150, and then the first moving unit 153 may move the firstsuction head 151 to the stack table 110 so as to allow the first suctionhead 151 to stack the first electrode 11 on the stack table 110.

The second electrode stack unit 160 may also be structured to stack thesecond electrode 12 on the stack table 110. The second electrode stackunit 160 may have the same structure as that of the foregoing firstelectrode stack unit 150. In such case, the second electrode stack unit160 may include a second suction head 161 and a second moving unit 163.The second suction head 161 may pick up the second electrode 12 seatedon the second electrode seating table 141 via vacuum suction. The secondmoving unit 163 may then move the second suction head 161 to the stacktable 110 so as to allow the second suction head 161 to stack the secondelectrode 12 on the stack table 110.

The stack table 110 may be rotatable so as to rotate between positionsfacing the first electrode stack unit 150 and the second electrode stackunit 160. As the stack table 110 rotates, the holding mechanism 170 mayhold the stack being assembled (comprising the first electrode 11, thesecond electrode 12, and the separator 14) in order to secure theposition of the stack relative to the stack table 110. For example, theholding mechanism 170 may apply downward pressure to the upper surfaceof the stack to press it towards the stack table 110. The holdingmechanism 170 may include, for example, a first holder 171 and a secondholder 172 to fix opposing sides of the first electrode 11 or the secondelectrode 12. The holders 171, 172 may each be in the form of one ormore clamps or other clamping mechanisms.

Thus, in operation, the first electrode 11 is supplied from the firstelectrode supply unit 130 to the first electrode stack unit 150, thefirst electrode stack unit 150 stacks the first electrode 11 on theupper surface of the separator 14 stacked on the stack table 110. Theholding mechanism 170 then presses down on the upper surface of thefirst electrode 11 to secure the position of the first electrode 11 onthe stack table 110. Thereafter, the stack table 110 is rotated in thedirection of the second electrode stack unit 160 while the separator 14is continuously supplied so as to cover the upper surface of the firstelectrode 11. Meanwhile, the second electrode 12 is supplied from thesecond electrode supply unit 140 and is stacked by the second electrodestack unit 160 on a portion of the separator 14 where the separator 14covers the upper surface of the first electrode 11. Then the holdingmechanism 170 releases the upper surface of the first electrode 11 andthen presses down on the upper surface of the second electrode 12 tosecure the position of the stack S being built vis-a-vis the stack table110.

Thereafter, by repeating the process of stacking the first electrode 11and the second electrode 12, the stack S in which the separator 14 iszig-zag-folded and positioned between each of the successive first andsecond electrodes 11, 12 may be formed.

After the components of the electrode assembly are stacked, theelectrode assembly may undergo one or more heat press operations. Inparticular, the electrode assembly may be moved to the press unit 180,which applies heat and pressure to the stack by advancing heatedpressing blocks 181 and 182 towards one another with the stackpositioned therebetween. As a result, the components of the stack (i.e.,the electrodes and separator) are thermally bonded to one another, so asto desirably prevent the completed electrode assembly from falling apartor the components of the electrode assembly from shifting theirpositions within the stack.

The heat press operations applied to the electrode assembly may includea primary heat press operation and a secondary heat press operation. Theprimary heat press relates to an operation after the first electrode(s)and the second electrode(s) are alternately stacked between the foldedseparators to define a stack, where the stack is gripped with a gripper,and then the stack is heated and pressed. The secondary heat pressoperation relates to an operation after the primary heat pressoperation, in which the gripping of the stack by the gripper is ceasedand the stack is once more heated and pressed.

Referring to FIG. 7 , the method may first include a stack process ofassembling a stack (stack cell) on a stack table by alternately stackingthe first electrode and the second electrode on the separator, where theseparator is continuously supplied and sequentially folded over apreviously-stacked one of the first and second electrodes before asubsequent one of the first and second electrodes is stacked. After thestack process, the stack may be moved way from the stack table. Duringsuch time, the separator is pulled, and, after the separator is pulledfor a predetermined length, the separator is cut. Thereafter, thepredetermined length of he cut end of the separator is wound around thestack cell. The movement of the stack away from the stack table may beaccomplished by the gripper, which is desirably a movable component thatcan grip the stack on the stack table and then move the stack to thepress unit 180, where the heat press operations are performed. Theprimary heat press operation is then performed in a state in which thewound stack cell is gripped with the gripper. After the primary heatpress operation is completed, the grip of the stack cell by the gripperis released. After the gripper is removed, the secondary heat pressoperation is performed. When the secondary heat press operation iscompleted, the finished electrode assembly may be complete.

When the temperature, pressure, and time conditions disclosed herein arenot satisfied, the components of the electrode assembly may not beproperly adhered together, which can result in the electrode assemblyfalling apart or the components of the electrode assembly shifting theirpositions within the assembly, particularly when the electrode assemblyis moved before being inserted into a battery case. A problem may alsooccur in which the air permeability of the separator is excessivelyhigh.

On the other hand, when the heat press operations disclosed herein areperformed (including satisfying the respective pressure, temperature,and time conditions), an electrode assembly may be manufactured withoutthe need to individually heat and/or press each level of the electrodeassembly (i.e., heating and/or pressing each electrode and separatorpair at each step of the process) in order to bond the componentstogether. Such individual heat pressing at each level can detrimentallycause the effects of the heat and/or pressure to accumulate in the lowerseparators in the stack, since the already-stacked layers willexperience the heat and/or pressure of each application. That cannegatively impact such portions of separator by, for example, reducingporosity (and air permeability). In contrast, the present inventionallows the entire electrode assembly to be simultaneously bonded, whichimproves uniformity, among other things. It is thus possible tosimultaneously achieve both an appropriate level of adhesive forcebetween the electrodes and also achieve a separator having anappropriate amount of air permeability, all while minimizing damage tothe unit electrode.

In the present application, the “air permeability” of the electrodeassembly refers to the air permeability of the separator component ofthe electrode assembly. In addition, unless specifically stated, the“air permeability” means air permeability of all separators comprisingthe electrode assembly, where the air permeability of each separator maybe independently the same or different.

In general, when the air permeability is less than 40 sec/100 ml, thespeed of lithium ion movement in the separator is increased, but therecan be a problem in that the safety of the electrode assembly may berapidly reduced, and there can also be a problem in that the speed ofthe lithium ion movement in the electrode(s) in the electrode assemblymay not correspond to the speed of the lithium ion movement in theseparator. Further, when the air permeability is greater than 120sec/100 ml, the speed of lithium ion movement in the separator islowered, which may reduce efficiency and performance of charging anddischarging cycles.

Thus, regardless of position within the electrode assembly, theseparator desirably has an air permeability in a range from 40 sec/100ml to 120 sec/100 ml.

The electrode assembly according to the present invention preferably hashigher air permeability than electrode assemblies in the related art,thereby increasing the safety of the electrode assembly. Specifically,the upper surface air permeability and the lower surface airpermeability of the electrode assembly according to the presentinvention may each independently be in a range from 80 sec/100 ml to 120sec/100 ml.

In accordance with the present invention, the method for measuring theair permeability of the separator is not particularly limited, and theair permeability may be measured by using a method commonly used in theart. For example, a Gurley type Densometer (No. 158) manufactured byToyoseiki may be used according to the JIS Gurley measurement method ofthe Japanese industrial standard. That is, the air permeability of theseparator may be obtained by measuring the time it takes for 100 ml (or100 cc) of air to pass through the separator of 1 square inch under apressure of 0.05 MPa at room temperature (i.e., 20° C. to 25° C.).

According to exemplary embodiments of the present invention, the middleair permeability of the electrode assembly may be in a range from 70sec/100 ml to 85 sec/100 ml, preferably from 75 sec/100 ml to 85 sec/100ml.

According to exemplary embodiments of the present invention, the uppersurface air permeability of the electrode assembly may be in a rangefrom 80 sec/100 ml to 120 sec/100 ml, preferably from 80 sec/100 ml to110 sec/110 ml, more preferably from 80 sec/100 ml to 100 sec/100 ml.

According to exemplary embodiments of the present invention, the lowersurface air permeability of the electrode assembly may be in a rangefrom 80 sec/100 ml to 120 sec/100 ml, preferably from 80 sec/100 ml to110 sec/110 ml, more preferably from 80 sec/100 ml to 100 sec/100 ml.

According to exemplary embodiments of the present invention, the lowersurface air permeability may be less than or equal to the upper surfaceair permeability. In addition, the middle air permeability may be lessthan or equal to the lower surface air permeability.

That is, the magnitude of the upper surface air permeability, the lowersurface air permeability, and the middle air permeability may satisfyEquation 1 below.

Upper surface air permeability≥Lower surface air permeability≥Middle airpermeability  [Equation 1]

The values of air permeability in Equation 1 relate to the airpermeability of the separators in the electrode assembly after thecompletion of the heating and pressing steps.

According to exemplary embodiments of the present invention, theadhesive force between the separator and the electrodes at any of thepositions in the electrode assembly (i.e., upper surface, middle, andlower surface) may be in a range from 5 gf/20 mm to 75 gf/20 mm.

In the present invention, a method for measuring adhesive force of theseparator is not particularly limited. For example, samples of the lowerportion, the middle portion, and the upper portion of the electrodeassembly may be separated from the stack. Such samples may include apositive electrode and a separator or a negative electrode and aseparator. The samples, which may have a width of 55 mm and a length of20 mm, are each adhered to a respective slide glass with the electrodebeing positioned on the adhesive surface of the slide glass. The samplesare then each tested by performing a 90° peel test at a speed of 100mm/min pursuant to the testing method set forth in ASTM-D6862. That is,an edge of the separator is pulled upwardly at 90° relative to the slideglass at a speed of 100 mm/min so as to peel the separator away from theelectrode along the width direction of the sample (i.e., peeling from 0mm to 55 mm).

According to exemplary embodiments of the present invention, the middleadhesive force of the electrode assembly may be in a range from 5 gf/20mm to 35 gf/20 mm, preferably from 5 gf/20 mm to 15 gf/20 mm.

According to exemplary embodiments of the present invention, the uppersurface adhesive force of the electrode assembly may be in a range from5 gf/20 mm to 75 gf/20 mm, preferably from 6 gf/20 mm to 30 gf/20 mm.

According to exemplary embodiments of the present invention, the lowersurface adhesive force of the electrode assembly may be in a range from5 gf/20 mm to 75 gf/20 mm, preferably from 9 gf/20 mm to 30 gf/20 mm.

According to exemplary embodiments of the present invention, the lowersurface adhesive force and the upper surface adhesive force may begreater than the middle adhesive force.

According to exemplary embodiments of the present invention, theadhesive force between the positive electrode and the separator and theadhesive force between the negative electrode and the separator may bethe same as or may be different from each other.

According to exemplary embodiments of the present invention, a deviationbetween the middle adhesive force of the electrode assembly and eitherthe upper surface adhesive force or the lower surface adhesive force ofthe electrode assembly may be in a range from 10 gf/20 mm to 35 gf/20mm, preferably from 10 gf/20 mm to 20 gf/20 mm.

According to exemplary embodiments of the present invention, a deviationbetween the middle air permeability of the electrode assembly and eitherthe upper surface air permeability or the lower surface air permeabilityof the electrode assembly may be in a range from 3 sec/100 ml to 15sec/100 ml.

When the air permeability and adhesive force conditions described aboveare satisfied, it may preferably make cleaning and process handlingeasy, and it may also make wetting of the separator by the electrolyteeasier, so that an electrode assembly having uniform performance may bemanufactured. In addition, side-effects, such as lithium (Li)precipitation in the electrode assembly and non-charging of theelectrode assembly, may be prevented.

A withstand voltage of the electrode assembly of the present inventionmay be in a range from 1.56 kV to 1.8 kV. The electrode assembly of thepresent invention is manufactured by the method of manufacturing theelectrode assembly including the primary heat press operation and thesecondary heat press operation, which may result in both excellentadhesive force and excellent withstand voltage compared to the casewhere only the primary heat press operation is performed.

According to the exemplary embodiment of the present invention, when itis assumed that a thickness of the uppermost electrode is 100%, it ispossible to provide an electrode assembly in which the thicknesses ofall electrodes are 70% to 120% of the thickness of the uppermostelectrode.

According to the exemplary embodiment of the present invention, theminimum thickness of the electrode of the electrode assembly may be 8.2mm or more.

According to the exemplary embodiment of the present invention, athickness deviation of the electrodes of the electrode assembly may bein a range from 0.013 mm to 0.035 mm.

When the thicknesses of the electrodes comprising the electrode assemblyare small and the thickness deviations between the electrodes are small,the electrode assembly may tend to be more structurally stable and morestable in use. As a result of the present invention, it is beneficiallypossible to manufacture an electrode assembly in which the thicknessesof the electrodes comprising the electrode assembly are small and thethickness deviations between the electrodes are small.

Although the present invention has been described in detail throughspecific exemplary embodiments, the present invention is not limitedthereto. Various different implementations may be made by those ofordinary skill in the art within the technical spirit of the presentinvention.

1) Example 1

19 positive electrode sheets, 20 negative electrode sheets, and anelongated separator were supplied to the stack table from the respectivepositive electrode supply unit, negative electrode supply unit, andseparator supply unit.

More specifically, the positive electrode and the negative electrodewere supplied after being cut from a positive electrode sheet and anegative electrode sheet, respectively, and the separator was suppliedin the form of an elongated separator sheet. Thereafter, the suppliedseparator was folded while rotating the stack table and stacking thepositive electrodes and the negative electrode as described above. Aholding mechanism was used to press down on and stabilize the stack,which resulted in a stack including 39 electrodes.

After assembling the stack, a primary heat press operation was performedby gripping the stack with the gripper and pressing for 15 seconds whileheating the stack under a temperature condition of 70° C. and a pressurecondition of 1.91 MPa.

After the primary heat press operation, the gripper was released fromthe stack and the secondary heat press operation was performed, in whicha pressing block was heated to a temperature of 70° C. (temperaturecondition), and a pressure of 2.71 Mpa (pressure condition) was appliedto the stack with the heated pressing block for 10 seconds (press time),thus resulting in the electrode assembly of Example 1.

In the process of manufacturing the electrode assembly, theabove-described disclosure of the present invention may be applied.

2) Examples 2 and 3

Electrode assemblies of Examples 2 and 3 were manufactured in the samemanner as in Example 1, except that the method was performed under thetemperature conditions, pressure conditions, and press time representedin Table 1 below.

TABLE 1 Primary heat press Temperature Pressure condition conditionPress area (314.57 cm²) Press time (° C.) Tonf MPa (s) Example 1 70 61.91 15 Example 2 Example 3 Secondary heat press Temperature Pressurecondition condition Press area (554.1 cm²) Press time (° C.) Tonf MPa(s) Example 1 70 5 2.71 10 Example 2 60 4 2.17 20 Example 3 80 4 2.17 20

3) Comparative Examples 1 to 7

Electrode assemblies of Comparative Examples 1 to 7 were manufactured inthe same manner as in Example 1, except that the primary heat pressoperation was performed under the temperature conditions, pressureconditions, and press time represented in Table 2 below, and thesecondary heat press operation was not performed.

TABLE 2 Primary heat press Temperature Pressure condition conditionPress area Press time (° C.) Tonf MPa (s) Comparative 70 6 1.91 15Example 1 Comparative 80 6 1.91 15 Example 2 Comparative 80 8 2.54 8Example 3 Comparative 80 8 2.54 15 Example 4 Comparative 90 6 1.91 15Example 5 Comparative 90 8 2.54 8 Example 6 Comparative 90 8 2.54 5Example 7 Secondary heat press (not performed) Temperature Pressurecondition condition Press area (554.1 cm²) Press time (° C.) Tonf MPa(s) Comparative — — — — Example 1 Comparative — — — — Example 2Comparative — — — — Example 3 Comparative — — — — Example 4 Comparative— — — — Example 5 Comparative — — — — Example 6 Comparative — — — —Example 7

4) Experimental Example 1—Thickness Measurement

The maximum thicknesses, minimum thicknesses, and average thicknesses ofthe electrodes configuring the electrode assemblies of Examples 1 to 3and Comparative Example 1, as well as the thickness deviations of theelectrodes, were measured by using a plate thickness measurement deviceequipped with a load cell.

In particular, the thickness when the upper plate of the plate thicknessmeasurement device is lowered and came into contact with the lower platewas set as 0 mm. Then, the electrode assembly of which the thickness wasto be measured was placed inside the plate thickness measurement device,and the plate was further lowered by applying a pressing force of 90 kgfover the area of the electrodes for 3 seconds, after which the platethickness was measured. In Example 1, the area to which the 90 kgf wasapplied was 554.1 cm².

The results are represented in Table 3.

TABLE 3 Thickness (mm) Maximum Minimum Average (Max) (Min) (AVG)Deviation Example 1 8.266 8.237 8.256 0.029 Example 2 8.265 8.251 8.2580.014 Example 3 8.237 8.205 8.216 0.032 Comparative 8.357 8.349 8.3520.008 Example 1

From the results of Table 3, it could be confirmed that, in theelectrode assembly according to the present invention, the thickness ofthe electrodes were small, and there was an appropriate amount ofthickness deviation between the electrodes.

It is believed that this is because the electrode assembly of thepresent invention was manufactured by the manufacturing method includingboth the primary and secondary heat press operations.

5) Experimental Example 2—Evaluation of Air Permeability

The air permeability of the electrode assemblies of Examples 1 to 3 andComparative Example 1 was evaluated.

Specifically, after collecting the separators in the electrodeassemblies of Examples 1 to 3, and Comparative Example 1, the separatorswere cut to prepare separator samples having a size of 5 cm×5 cm(width×length). After that, the separator samples were washed withacetone.

Air permeability of Examples 1 to 3 and Comparative Example 1 weremeasured by measuring the time it took for 100 ml (or 100 cc) of air topass through the separator of 1 square inch at room temperature andunder the pressure condition of 0.05 MPa by using a Gurley typeDensometer (No. 158) from Toyoseiki in accordance with the JIS Gurleymeasurement method of the Japanese industrial standard.

The results are represented in Table 4.

TABLE 4 Air permeability (sec/100 ml) Upper surface Middle Lower surfaceDeviation Example 1 88 76 84 11.1 Example 2 88 75 87 12.3 Example 3 10184 100 17.4 Comparative 76 74 77 3.0 Example 1

From the results of Table 4, it was confirmed that the upper surface airpermeability and the lower surface air permeability of the electrodeassembly according to the present invention were each independently 80sec/100 ml or more. Further, it was confirmed that the upper surface airpermeability and the lower surface air permeability of the electrodeassembly according to the present invention did not exceed 120 sec/100ml. That is, it could be confirmed that the electrode assembly accordingto the present invention has an appropriate level of air permeabilityfor use as an electrode assembly.

In addition, it was confirmed that the air permeability deviationbetween each location was less than 20 sec/100 ml, which was consideredto be substantially uniform.

On the other hand, in the case of Comparative Example 1, the deviationin air permeability between each location was smaller than that of theExample, but it could be confirmed that the upper surface airpermeability and the lower surface air permeability were eachindependently less than 80 sec/100 ml, so that safety was lower thanthat of the electrode assembly according to the present invention. It isbelieved that this is because only the primary heat press was performeddifferently from the manufacturing process of the electrode assembly ofthe present invention.

6) Experimental Example 3—Adhesive Force Evaluation and WithstandVoltage Evaluation

The electrode assemblies of Examples 1 to 3 and Comparative Examples 1to 7 were disassembled and analyzed to measure upper surface, lowersurface, and middle adhesive force. Specifically, adhesive force betweenthe negative electrode and the separator located at the lowermost end ofthe stack was measured. Additionally, adhesive force between thenegative electrode and the separator located at the uppermost end of thestack was measured. Finally, adhesive force between the negativeelectrode and the separator located at a middle location along thestacking direction of the stack was measured.

In each of the separated electrode assemblies, the negative electrodeand the separator sampled had a width of 55 mm and a length of 20 mm.The sampled sample was adhered to the slide glass with the electrodebeing positioned on the adhesive surface of the slide glass. After that,the slide glass with the sample was mounted to the adhesive forcemeasuring device and tested by performing a 90° peel test at a speed of100 mm/min pursuant to the testing method set forth in ASTM-D6862. Thatis, an edge of the separator was pulled upwardly at 90° relative to theslide glass at a speed of 100 mm/min so as to peel the separator awayfrom the electrode along the width direction of the sample (i.e.,peeling from 0 mm to 55 mm). After discounting any initial significantfluctuations, the values for applied force per sample width (ingrams/mm) were measured while the separator was peeled away from theelectrode.

The results are represented in Table 5 below.

TABLE 5 Negative electrode adhesive force (gf/20 mm) Upper surfaceMiddle Lower surface Deviation Example 1 19.8 10.8 21.5 10.7 Example 211.1 7.1 14.3 7.2 Example 3 25.3 12.0 22.4 13.3 Comparative 9.8 5.8 11.25.5 Example 1 Comparative 15.6 6.9 15.8 8.9 Example 2 Comparative 14.55.6 16.5 10.9 Example 3 Comparative 19.5 9.0 21.2 12.2 Example 4Comparative 19.5 13.8 24.2 10.4 Example 5 Comparative 15.6 7.2 25.9 18.7Example 6 Comparative 30.7 12.6 25.1 18.1 Example 7

In addition, the withstand voltages of the electrode assemblies ofExamples 1 to 3 and Comparative Examples 1 to 7 were also measured.

The results are represented in Table 6 below.

TABLE 6 Withstand voltage (kV) Example 1 1.58 Example 2 1.56 Example 31.58 Comparative Example 1 1.82 Comparative Example 2 1.51 ComparativeExample 3 1.49 Comparative Example 4 1.47 Comparative Example 5 1.48Comparative Example 6 1.45 Comparative Example 7 1.45

Investigating the results of Table 5, it was confirmed that the adhesiveforce of Examples 1 to 3 was superior to that of Comparative Example 1,in which only the primary heat press operation was performed underconditions similar to those of the Examples.

In addition, investigating the results of Table 6, it was confirmed thatthe withstand voltage of Examples 1 to 3, in which the primary heatpress operation was performed under higher temperature and higherpressure conditions than those of the Comparative Examples had a rangeof 1.56 kV or more and 1.8 kV or less.

That is, the electrode assembly of the present invention has excellentadhesive force and, at the same time, has a withstand voltage suitablefor use as an electrode assembly. In that regard, a withstand voltage of1.8 kV or less was confirmed.

It is believed that this is because the electrode assembly wasmanufactured by the manufacturing method including both the primary andsecondary heat press operations.

7) Experimental Example 4

After charging the electrode assemblies of Example 1 and ComparativeExample 1 was completed, the electrode assemblies were disassembled tocheck whether lithium (Li) was precipitated. The results are representedin FIGS. 5 and 6 .

In the case of the electrode assembly of Comparative Example 1, it wasconfirmed that lithium (Li) was precipitated upon disassembly after theelectrode assembly was completely charged as illustrated in FIG. 5 .

In the case of the electrode assembly of Example 1, it was confirmedthat lithium (Li) was not precipitated upon disassembly after theelectrode assembly was completely charged, as illustrated in FIG. 6 .

It is believed that this is because the electrode assembly wasmanufactured by the manufacturing method including both the primary andsecondary heat press.

Through Experimental Examples 1 to 3, it could be confirmed that theelectrode assembly according to the present invention has an appropriatewithstand voltage while also having excellent stability and adhesiveforce, and is possible to prevent side-effects, such as lithium (Li)precipitation in the electrode assembly and non-charging of theelectrode assembly.

What is claimed is:
 1. An electrode assembly, comprising: a plurality ofelectrodes arranged in a stack along a stacking axis with a respectiveseparator portion positioned between each of the electrodes in thestack, the plurality of electrodes including a top one of the pluralityof electrodes positioned at a top of the stack along the stacking axisand including a bottom one of the plurality of electrodes positioned ata bottom of the stack along the stacking axis, wherein the bottomelectrode has a thickness along the stacking axis that is from 80% to120% of a thickness of the top electrode along the stacking axis, andwherein a maximum thickness of each of the electrodes in the stack isless than 8.3 mm.
 2. The electrode assembly of claim 1, wherein theseparator portions are portions of an elongated separator sheet, theelongated separator sheet being folded between each separator portionsuch that the elongated separator sheet follows a serpentine pathtraversing back and forth along an orthogonal dimension orthogonal tothe stacking axis to extend between each of the successive electrodes inthe stack.
 3. The electrode assembly of claim 1, wherein the thicknessof each of the electrodes in the stack has a thickness along thestacking axis that is from 70% to 120% of a thickness of the topelectrode along the stacking axis.
 4. The electrode assembly of claim 3,wherein a minimum thickness of each of the electrodes of the electrodeassembly is 8.2 mm.
 5. The electrode assembly of claim 1, wherein theplurality of electrodes include an intermediate one of the plurality ofelectrodes between the top electrode and the bottom electrode along thestacking axis, wherein the separator portions include an intermediateone of the separator portions abutting the intermediate electrode, andwherein the intermediate separator portion is adhered to theintermediate electrode to a degree that it would take a peel force in arange from 5 gf to 35 gf per 20 mm width of the intermediate separatorportion applied to an edge of the intermediate separator portion inorder to peel the intermediate separator portion away from theintermediate electrode at a speed of 100 mm/min along the stacking axis.6. The electrode assembly of claim 1, wherein the separator portionsinclude a top one of the separator portions abutting the top electrode,and wherein the top separator portion is adhered to the top electrode toa degree that it would take a peel force in a range from 5 gf to 70 gfper 20 mm width of the top separator portion applied to an edge of thetop separator portion in order to peel the top separator portion awayfrom the top electrode at a speed of 100 mm/min along the stacking axis.7. The electrode assembly of claim 1, wherein the separator portionsinclude a top one of the separator portions abutting the top electrode,and wherein the top separator portion has a value of air permeabilityfrom 80 sec/100 ml to 120 sec/100 ml per square inch of the respectiveseparator portion at a pressure of 0.05 MPa.
 8. The electrode assemblyof claim 1, wherein the separator portions include a bottom one of theseparator portions abutting the bottom electrode, and wherein the bottomseparator portion is adhered to the bottom electrode to a degree that itwould take a peel force in a range from 5 gf to 75 gf per 20 mm width ofthe bottom separator portion applied to an edge of the bottom separatorportion in order to peel the bottom separator portion away from thebottom electrode at a speed of 100 mm/min along the stacking axis. 9.The electrode assembly of claim 1, wherein the separator portionsinclude a bottom one of the separator portions abutting the bottomelectrode, and wherein the bottom separator portion has a value of airpermeability from 80 sec/100 ml to 120 sec/100 ml per square inch of therespective separator portion at a pressure of 0.05 MPa.
 10. Theelectrode assembly of claim 1, wherein the plurality of electrodesinclude an intermediate one of the plurality of electrodes positionedbetween the top electrode and the bottom electrode along the stackingaxis, wherein the separator portions include: an intermediate one of theseparator portions abutting the intermediate electrode, a top one of theseparator portions abutting the top electrode, and a bottom one of theseparator portions abutting the bottom electrode, wherein theintermediate separator portion is adhered to the intermediate electrodeto a degree that it would take a first peel force per 20 mm width of theintermediate separator portion applied to an edge of the intermediateseparator portion in order to peel the intermediate separator portionaway from the intermediate electrode at a speed of 100 mm/min along thestacking axis, wherein the top and bottom separator portions are adheredto the respective top and bottom electrodes to a degree that it wouldtake a second peel force per 20 mm width of the respective top andbottom separator portions applied to an edge of the respective top andbottom separator portion in order to peel the respective top and bottomseparator portion away from the respective top and bottom electrode at aspeed of 100 mm/min along the stacking axis, and wherein a differencebetween the first peel force and the second peel force is from 3 gf/20mm to 15 gf/20 mm.
 11. The electrode assembly of claim 1, wherein theplurality of electrodes include an intermediate one of the plurality ofelectrodes positioned between the top electrode and the bottom electrodealong the stacking axis, wherein the separator portions include: anintermediate one of the separator portions abutting the intermediateelectrode, a top one of the separator portions abutting the topelectrode, and a bottom one of the separator portions abutting thebottom electrode, wherein the intermediate separator portion has asecond value of air permeability per square inch at a pressure of 0.05MPa and at room temperature, and wherein the difference between thesecond value of air permeability and the value of air permeability ofthe top separator portion and the bottom separator portion is from 10sec/100 ml to 35 sec/100 ml per square inch of the respective separatorportion at a pressure of 0.05 MPa and at room temperature.